The present invention relates to a force sensor and, more particularly, to a force sensor which also functions as a push-button switch.
Push-button switches are used as input means to input ON/OFF information into a variety of electric appliances. In particular, low priced push-button switches employing silicon rubber have been widely used as operational buttons in various remote controllers, cellular phones, game machines, etc. In such types of push-buttons, a bowl-shaped silicon rubber is arranged upside down on an electronic circuit board and the bottom of the bowl is depressed to contact with the electrode pattern on the circuit board. The state of contact is detected electrically to thereby recognize the ON/OFF state. The push-button switch of such a type can provide a long stroke that corresponds to the height of the bowl-shaped portion. The switch also can provide a unique click feeling obtained by the elastic deformation of the bowl-shaped silicon rubber. Thus, this makes it easier for an operator to intuitively recognize through the sense of touch as to whether it is in the ON or OFF state, thereby providing highly favorable operability.
On the other hand, force sensors have also been used as devices that convert the operational inputs of operators to electrical signals. Force sensors can input operational amounts having a predetermined dynamic range as the magnitude of a force applied by the operator, while the push-button switch described above can only input ON/OFF information. Two-dimensional or three-dimensional force sensors are also used which are capable of decomposing an applied force into directional components to detect the force. In particular, capacitance-type force sensors have been used in various fields since the sensors provide the advantages of simplified structure and reduced cost. The sensor has a capacitance element formed of two electrodes to detect force based on the change in capacitance resulting from the change in spacing between the two electrodes. For example, capacitance-type multidimensional force sensors are disclosed in Japanese Laid Open Patent Publication No. 4-148833 of 1992, No. 4-249726 of 1992, No. 4-299227 of 1992, No. 4-337431 of 1992.
As described above, push-button switches and force sensors have been used in different applications, but devices having both functions are expected to be in demand in the coming years. For example, as an input device for use with game machines, a device is used having a push-button switch and a force sensor, which are separately incorporated into the device. Here, the push-button switch is to input ON/OFF information and the force sensor (i.e., the so-called xe2x80x9cjoy-stickxe2x80x9d) is to perform operational input in multidimensional directions. However, in order to improve operability, the magnitude of an applied force as well as the ON/OFF operational input can be preferably detected by means of a single device.
An object of the present invention is to provide a force sensor that can recognize the magnitude of predetermined directional components of an applied force, while providing the function of a push-button switch that detects ON/OFF operational input. A further object of the present invention is particularly to provide a force sensor which provides a sufficient stroke and favorable click feeling to serve as a push-button and provides reduced cost as well.
According to the present invention, a force sensor is realized which detects a magnitude of a predetermined directional component of an applied force, while functioning as a push-button switch that detects the operational ON/OFF input.
(1) The first feature of the present invention resides in a force sensor comprising:
a circuit board arranged at a position where an upper surface thereof is contained in an X-Y plane when an XYZ three-dimensional coordinate system is defined;
an acting body attached to the upper surface of the circuit board, the acting body having a displacement portion arranged above the circuit board and displaced when an external force is applied thereto, a securing portion fixed to the circuit board, and a connecting portion for connecting the displacement portion to the securing portion;
an elastic deformation body, formed on a lower surface of the displacement portion and having elastic deformation properties;
a switch displacement electrode formed on a lower surface of the elastic deformation body;
a switch securing electrode formed on a position opposite to the switch displacement electrode on the circuit board; and
a capacitor adapted to produce a variation in capacitance caused by a displacement of the displacement portion;
wherein the connecting portion has flexibility so that when a force is applied to the displacement portion, a deflection is produced in the connecting portion, thereby causing a displacement in the displacement portion relative to the circuit board;
wherein when no force is applied to the displacement portion, the switch displacement electrode and the switch securing electrode are not kept in contact with each other, and when a force of a predetermined amount, directed in a Z-axis direction of the coordinate system, is applied to the displacement portion, the switch displacement electrode and the switch securing electrode are brought into contact with each other;
wherein when a further force, directed in the Z-axis direction, is applied to the displacement portion, the elastic deformation body is elastically deformed, thereby allowing capacitance of the capacitor to vary, with the contact state kept unchanged between the switch displacement electrode and the switch securing electrode; and
wherein a switch is composed of the switch displacement electrode and the switch securing electrode, and a contact state therebetween is electrically detected to thereby recognize the state of the switch and a change in capacitance of the capacitor is electrically detected to thereby recognize a magnitude of a predetermined directional component of a force applied.
(2) The second feature of the present invention resides in a force sensor according to the first feature:
wherein an acting body having a bowl-shaped portion is prepared and attached to the upper surface of the circuit board to be upside down, to use a portion corresponding to a bottom of the bowl as a displacement portion, to use a portion corresponding to a side of the bowl as a connecting portion, and to use a portion corresponding to a mouth of the bowl as a securing portion.
(3) The third feature of the present invention resides in a force sensor according to the second feature:
wherein an intermediate displacement board is disposed between the circuit board and the acting body so that a part of the intermediate displacement board is secured to the circuit board as a displacement board securing portion and another part of the intermediate displacement board constitutes a displacement board displacement portion for generating a displacement caused by a displacement in the displacement portion or a deformation in the connecting portion; and
a capacitor securing electrode formed on the circuit board and a capacitor displacement electrode formed on the displacement board displacement portion constitute a capacitor.
(4) The fourth feature of the present invention resides in a force sensor according to the third feature:
wherein a flexible plate having a bowl-shaped portion constitutes the intermediate displacement board, the intermediate displacement board being attached to the upper surface of the circuit board so as to arrange the bowl-shaped portion upside down, an open window being formed for allowing the elastic deformation body to penetrate therethrough on a portion corresponding to a bottom of the bowl, a portion surrounding the open window constituting the displacement board displacement portion, a portion corresponding to a mouth of the bowl constituting the displacement board securing portion, and the displacement portion or the connecting portion being brought into physical contact with the displacement board displacement portion to generate a displacement.
(5) The fifth feature of the present invention resides in a force sensor according to the fourth feature:
wherein the intermediate displacement board is made of a metal material and the intermediate displacement board itself is used as a capacitor displacement electrode.
(6) The sixth feature of the present invention resides in a force sensor according to the fourth feature:
wherein the intermediate displacement board is made of synthetic resin and a metal film formed on a lower surface thereof composes a capacitor displacement electrode.
(7) The seventh feature of the present invention resides in a force sensor according to the sixth feature:
wherein a first additional switch electrode is formed on an upper surface of the intermediate displacement board and a second additional switch electrode is formed at a position opposite to the first additional switch electrode provided on a lower surface of the displacement portion so that both of the additional switch electrodes constituting an additional switch and a contact state between the first additional switch electrode and the second additional switch electrode is electrically detected, thereby enabling to provide additional information regarding an applied force.
(8) The eighth feature of the present invention resides in a force sensor according to the seventh feature:
wherein when the Z-axis is defined at a center of the displacement portion, an additional switch is provided at a position located above a positive X-axis and another additional switch is provided at a position located above a negative X-axis, thereby enabling to provide information regarding an X-axis component of an applied force, based on a state of a pair of the additional switches.
(9) The ninth feature of the present invention resides in a force sensor according to the eighth feature:
wherein an additional switch is further provided at a position located above a positive Y-axis and another additional switch is further provided at a position located above a negative Y-axis, thereby enabling to provide information regarding a Y-axis component of an applied force, based on a state of a pair of the further additional switches.
(10) The tenth feature of the present invention resides in a force sensor according to the seventh feature:
wherein among a set of counter electrodes constituting the additional switch, one electrode is composed of a single electrode layer and the other electrode is composed of a pair of electrode layers, electrically independent of each other, and a conductive state between the pair of electrode layers is electrically detected, thereby enabling detection of a contact state of the counter electrodes.
(11) The eleventh feature of the present invention resides in a force sensor according to the first feature:
wherein a capacitor securing electrode formed on the upper surface of the circuit board and a capacitor displacement electrode formed on a lower surface of the displacement portion constitute a capacitor.
(12) The twelfth feature of the present invention resides in a force sensor according to the eleventh feature:
wherein wiring is provided for making the capacitor displacement electrode and the switch displacement electrode conductive therebetween so that when the switch displacement electrode and the switch securing electrode are brought into contact with each other, capacitance between the switch securing electrode and the capacitor securing electrode is measured to detect a capacitance of the capacitor.
(13) The thirteenth feature of the present invention resides in a force sensor according to the eleventh feature:
wherein when the Z-axis is defined at a center of the displacement portion, a first capacitor is provided at a position located above a positive X-axis and a second capacitor is provided at a position located above a negative X-axis so as to determine direction and magnitude of an X-axis component of an applied force based on a difference in capacitance between a pair of the first and second capacitors.
(14) The fourteenth feature of the present invention resides in a force sensor according to the thirteenth feature:
wherein a third capacitor is further provided at a position located above a positive Y-axis and a fourth capacitor is provided at a position located above a negative Y-axis so as to determine direction and magnitude of a Y-axis component of an applied force based on a difference in capacitance between a pair of the third and fourth capacitors.
(15) The fifteenth feature of the present invention resides in a force sensor according to the eleventh feature:
wherein a capacitor having an electrode formed to be generally symmetric with both the X- and Y-axes is provided so that a magnitude of a Z-axis component of an applied force can be determined based on capacitance of the capacitor.
(16) The sixteenth feature of the present invention resides in a force sensor according to the eleventh feature:
wherein two sets of capacitors including a signal input capacitor and a signal output capacitor are provided, respective capacitor securing electrodes of the two sets of capacitors are composed of separate electrodes electrically independent of each other and respective capacitor displacement electrodes of the two sets of capacitors are composed of a single common electrode electrically conductive with each other; and
periodic signal supply means for supplying a periodic signal to a capacitor securing electrode of the signal input capacitor and periodic signal detection means for detecting a periodic signal induced in a securing electrode of the signal output capacitor are provided so that a change in capacitance between the two sets of capacitors is obtained based on a magnitude of the periodic signal to be detected by means of the periodic signal detection means when the periodic signal of a predetermined magnitude is supplied by means of the periodic signal supply means.
(17) The seventeenth feature of the present invention resides in a force sensor according to the eleventh feature:
wherein an insulation film is formed on a surface of any one or both of a capacitor securing electrode and a capacitor displacement electrode.
(18) The eighteenth feature of the present invention resides in a force sensor according to the first feature:
wherein the switch displacement electrode is composed of a single electrode layer and the switch securing electrode is composed of a pair of electrode layers electrically independent of each other, and a contact state of the pair of the electrode layers is electrically detected so as to detect a contact state between the switch displacement electrode and the switch securing electrode.
(19) The nineteenth feature of the present invention resides in a force sensor according to the first feature:
wherein the elastic deformation portion is composed of a material having an elastic coefficient corresponding to detection sensitivity.
(20) The twentieth feature of the present invention resides in a force sensor according to the first feature:
wherein the elastic deformation portion is provided with a groove corresponding to detection sensitivity.
(21) The twenty-first feature of the present invention resides in a force sensor according to the first feature:
wherein the acting body and the elastic deformation portion are composed of a strain generative body integrally formed of rubber.